This invention relates to an improved episcopic image projection system, i.e., projection system which reflects light from a graphic sheet onto a screen or other suitable surface. Such systems are distinguished from diascopic image projection systems wherein light passes through the graphic sheet en route to the screen. Because light in the episcopic system does not have to pass through the graphic sheet, opaque graphic sheets rather than transparent graphic sheets can be utilized. For this reason episcopic image projection systems are commonly referred to as opaque projectors.
Opaque projectors have the inherent advantage that plain paper graphics, and even three-dimensional objects, can be projected without special preparation. This, of course, eliminates the time and expense needed to prepare transparencies of each graphic which are required in diascopic image projection systems. Moreover, the use of plain paper graphics in opaque projectors gives the user an element of spontaneity and versatility during a visual presentation which is not available in diascopic systems.
In spite of their many benefits, opaque projectors have had limited commercial acceptance and success. Numerous factors such as cost, size, weight, operation difficulties, image diffusion and the like may account for this situation.
Accordingly, there have been several attempts over the years to produce a compact opaque projector which is capable of achieving excellent optical results. Some of these attempts are described in U.S. Pat. Nos. 3,951,535; 3,947,103; 3,915,567; 3,837,739; 3,778,142; 3,512,883; 2,596,393; Re. No. 28,274; and Swedish Patent No. 172,201. Other image projection systems are disclosed in U.S. Pat. Nos. 3,900,253; 3,752,574; 3,366,005; 3,257,898; 3,190,174; and 1,988,522.
An improved portable opaque projector is described by U.S. Pat. No. 4,468,105. In the device described therein, which has both an operable mode and a portable mode, the hinged lid of the projector case is raised and secured at an acute angle with respect to the projection lens, and a reflecting mirror is then supported by the raised lid. However, a relatively large reflecting mirror is required because of the resulting configuration. Such a mirror is also subject to non-planar distortion and to vibration transmitted through the lid itself, which detract from the quality of the projected image. The size of the necessary mirror further detracts from the economy and portability of the resulting projector.
Accordingly, it is an object of this invention to provide an improved opaque projector, and particularly an improved portable opaque projector. Another object is the provision of such a projector which may have a completely removable lid, and which is sufficiently compact and portable to enable it to be readily stored and transported, yet sufficiently uncomplicated to be easy to assemble and use. A related object is to provide such an improved portable opaque projector which includes a stable means for mounting a reflecting mirror of minimum size, to enhance portability and minimize projected image distortion. A further object is to provide a mounting means for a reflecting mirror which allows use of a mirror of minimum dimensions in such a projector. Another object is to provide a mirror structure for such a projector which minimizes or eliminates non-planar distortions in the reflecting surface. Other objects, features and advantages of the invention will become apparent hereinafter.